Calcareous nannofossils as paleoproductivity indicators in upper cretaceous organic-rich sequences in Israel

Abundant and diverse calcareous nannofossil assemblages were found in organic-rich carbonate sequences which accumulated in a Campanian- Maastrichtian upwelling belt along the southeastern Tethys. The sequences studied represent the inner (shallower) and the outer (deeper) parts of the upwelling belt. The paleoenvironmental significance of selected nannofossil taxa and their utility in productivity reconstruction was established by comparing their distribution to foraminifera and dinocyst-based productivity profiles. Based on the calcareous nannofossil assemblages, a high- productivity group and a low-productivity group of species were determined. The distribution of these groups agrees well with the dinocyst- and foraminifera-based productivity curves and, hence, can be used to record paleoproductivity changes. The ratio between the high-productivity and low- productivity nannofossil groups, the Nannofossil Index of Productivity (NIP), is proposed here as a productivity proxy that can be utilized in reconstructing basinal productivity development. A quantitative analysis of the nannofossil assemblages indicates that their abundance and diversity increase towards the open sea, in the outer and less productive part of the upwelling belt. In the inner and more productive part of the upwelling belt, the nannofossils assemblages become less abundant and less diverse relative to those of the open marine environment. Micula decussata and Watznaueria barnesae are common to abundant in most samples. M. decussata becomes more abundant in poorly-preserved samples. On the other hand, the distribution of W. barnesae matches better with intermediate productivity levels.